Continuing investigation of the physiological significance of somatostatin. By means of collaborative arrangements, continuing investigation of possible therapeutic use of somatostatin in the management of several endocrinopathies. Synthesis and biological testing of structural analogues of somatostatin towards the following goals: a) Structure/function relationship studies; b) Obtain long acting or more potent analogues; c) Obtain antagonists; d) Obtain analogues which would have some activities of somatostatin and not others. For example, the pancreatropic effects of somatostatin might well preclude its chronic use in acromegalics; an analogue found with high hypophysiotropic and low pancreatropic potency would provide a solution to this problem. Physiology, purification and characterization of additional hypophysiotropic substances -- GRF, CRF and PIF -- which have been evidenced in our existing hypothalamic extracts.